CHAPTER XVI 

 THE CENTRAL ORGANIZATION OF VISION 



A consideration of the phylogenetic evolution of the central nervous organization 

 of vision is suitably introduced by a photograph of Cornelius ubbo ariens kappers 

 (1877-1946) (Fig. 665), Director of the Centraal Instituut voor Hersenonderzoek in 

 Amsterdam in 1909, and Professor of Xeuro -anatomy at the University of Amsterdam 

 in 1928. In his generation he was the greatest authority on the comparative structure 

 of the nervous system, and his magnuin opus. Die vergleichende Anatomie des Nerven- 

 systems der Wirbeltiere und des Menschen (1920), still remains the classical work on 

 this subject. His work was not alone concerned with the factual description of structure 

 but was enlivened and coordinated by much original thovight. AiTiong his speculative 

 concepts the best known is that of " neurobiotaxis," a hypothesis by which he 

 endeavoured to explain the complicated migration of nerve centres and tracts in 

 phylogenetic history, and the seemingly peculiar location and relation in which this 

 has resulted in the higher animals. This suggestion, that the final arrangement of 

 neural elements is determined by an association of function, perhaps on a physico- 

 chemical basis, is seen in many of those parts of the central nervous system which are 

 associated with visual and photostatic functions — the position, for example, of the 

 ocular motor nuclei in close relation to the posterior longitudinal bundle and the 

 vestibular systeni, their secondary changes in position running parallel to changes in 

 the paths of the optic, vestibular and coordinative reflexes, or the gradual development 

 of a decussation of fibres at the chiasma so that fibres from regions of the retinae which 

 work together run in contiguity. 



In the first chapters of this book we have seen that fight has a four-fold 

 action upon fiving organisms — upon the general metabolism including the 

 reproductive cycle, upon the control of movement, upon the retinal and 

 integumentary pigmentation, and upon behaviour, and eventually con- 

 sciousness, through visual sensations. In the more primitive animals the 

 first two assume the greatest importance, in the higher the last becomes 

 completely dominant, while the third always plays a somewhat subsidiary 

 role. It is obvious, however, that none of these can become effective unless 

 the local effects of the photochemical reaction mitiated by light are made 

 available to the organism as a whole and coordinated with its general 

 activities. For this purpose two mechanisms are available — in the first the 

 effects of the stimulus are conveyed by chemical means, in the second by 

 nervous conduction. 



The problems of communication and coordmation were relatively 

 simple in unicellular organisms, but unless evolution were not to pass beyond 

 the stage of colonial Protozoa or the sponges and confine itself to entities 

 comprised of loosely aggregated and relatively independent cells, rapidity of 

 communication and control became essential for the development of a 

 multicellular body with all its potentialities of specialization in structure 

 and function. The evolution of an efficient conductmg mechanism was thus 



